The Burden of Life
In the Kanneliya-Dediyagala-Nakiyadeniya (KDN) forest complex, a UNESCO Biosphere Reserve, the branches of trees tell a story of extreme ecological collaboration. This lowland wet evergreen forest receives an average annual rainfall of about 3,750 mm, creating a perpetually humid environment ideal for epiphytes—plants that grow on other plants without being parasitic. These non-parasitic plants, including thousands of orchid, fern, and moss species, use host trees as anchors to reach the sunlit upper canopy. They derive moisture and nutrients from the air, rain, and the debris that collects around their own roots.
The sheer mass of these arboreal communities is immense. In some tropical montane cloud forests, the weight of epiphytes on a single tree can reach several tonnes. While specific biomass measurements for Kanneliya are not widely published, the observed phenomenon of branches, and sometimes entire trees, collapsing under the load is evidence of the biomass these epiphytes can accumulate. The accumulated weight comes from the plants themselves but also from the "canopy soil" they create—a absorbent mat of decaying organic matter, trapped moisture, and microorganisms. This soil can hold many times its own weight in water, adding a significant and fluctuating burden to the host tree's limbs after every downpour.
A Canopy Ecosystem
The dominant trees in Kanneliya's climax forest community belong to the Shorea, Dipterocarpus, and Mesua genera. These trees form the structural foundation for a complex, layered ecosystem. The epiphyte load is an important part of this system. The canopy soil they form retains nutrients that would otherwise be washed away, slowly releasing them for the host tree and other organisms to use. Many animal species, from insects and amphibians to birds and small mammals, live their entire lives within these treetop gardens.
Kanneliya is one of the most floristically diverse areas in South Asia. The forest contains over 300 plant species, with 52 percent of its 319 woody plants being endemic to Sri Lanka. Among the epiphytes are numerous rare and endemic orchids and ferns, such as the coarse tassel fern (Lycopodium squarrosum). The forest's high humidity and stable temperatures, averaging 27°C, allow these specialized plants to thrive. This heavy growth, while ecologically productive, puts immense physical stress on host trees. The constant weight, amplified by wind and rain, can lead to "epiphyte-induced tree fall," a natural process that creates gaps in the canopy, allowing light to reach the forest floor and spur new growth.